Various approaches have been devised for detecting, monitoring and measuring the amount of wear which has occurred to a wear member. For example, in the area of rotating equipment, a number of electrical devices are available to detect and monitor bearing wear. These devices are based upon a number of detection techniques. Thus, wear detection might depend upon the completion of an electrical circuit through the bearing when there is excessive bearing wear, or it might depend upon the generation of a voltage if the shaft rotates eccentrically, or it might depend upon the detection of an abnormal temperature rise of the bearing. Each of these approaches has some inherent disadvantages with respect to accuracy and does not measure actual bearing wear, bearing wall thickness or the amount of material which has been removed from the bearing, i.e., each approach is responsive to bearing wear but does not measure quantitatively the amount of wear that has occurred, the wall thickness remaining or the amount of material which has been removed.
Other approaches have been devised to measure the thickness of a workpiece or wear member, and by measuring such thickness, the amount of wear which has occurred can be calculated. These approaches have numerous commercial and/or industrial applications, however, their use for measuring the thickness of or wear which has occurred to a work surface in-situ is cost prohibitive. In addition, these approaches typically utilize devices fabricated from materials which limit their applications to an operating environment having a temperature of normally less than 75.degree. C., and cause the resulting readings to be dependent upon the temperature of the operating environment. It has also been found that the materials utilized for these devices cannot withstand severe operating environments which further limits the applications in which they can be used. Thus, these devices and measurement techniques are not usable for measuring and/or monitoring the thickness of or wear which has occurred to work surfaces, such as a sleeve bearing, in an elevated temperature operating environment such as might exist in rotating equipment. This inability to measure and/or monitor wear in-situ can result in costly machine downtime to inspect the condition of the bearings. Alternatively, this inability can result in unnecessary damage to the rotating equipment due to bearing failure which was not promptly detected.
Because of the foregoing, it has become desirable to develop a device which can be utilized to measure and/or monitor in-situ the thickness of, the amount of wear which has occurred to, and the amount of material which has been removed from a member such as sleeve or thrust bearings, brake discs or pads, clutch plates and sealing members. Ideally, the resulting device could also be used for measuring other physical properties (such as temperature or pressure) of the member, in-situ, and positional properties of the member relative to other members or surfaces defining same.